The long-term objective of this research is to identify who develops posttraumatic stress symptoms when they are exposed to a traumatic event and who does not;and to understand why one person does and another does not. The research focuses on urban adolescents at the end of high-school because older adolescents living in large cities are the group of people who are most exposed to potentially traumatic events. The basic idea underlying the research is that the level of posttraumatic stress symptoms that an individual exhibits depends upon the degree to which she has experienced traumatic events and the degree to which she possesses certain characteristics that protect her from stress. The present study uses a "person-centered" approach. It proposes to classify individuals into groups in which the individuals in a given group are similar to each other, but different from individuals in other groups, in terms of the combination of exposure to potentially traumatic events and manifesting posttraumatic stress symptoms. This classification will be done by a relatively sophisticated statistical procedure, latent class analysis. Four prototypical groups are expected to be produced by this analysis. They are (with tentative labels): 1) high trauma and high symptoms (people with Posttraumatic Stress);2) high trauma and low symptoms (people who are Resilient);3) low trauma and high symptoms (people who are Stress Prone);and 4) low trauma and low symptoms (the Idealized Norm for people in our society). Two of the goals of the research are to determine whether or not people really do fit into these prototypical categories, and if they do, to determine the proportion of people in each category. The third goal of the research is to determine whether or not, and how, these four categories of people are different in terms of the pattern of protective characteristics that they possess. This goal will be accomplished by the use of the statistical procedures multivariable analysis of variance and multiple discriminant analysis. Psychopathology associated with exposure to traumatic events is arguably the most common mental health problem. The identification of the relative numbers of people in each of the four prototypical categories of this phenomenon and the increased understanding of the psychosocial dynamics that produce the membership in the categories will provide an expanded foundation for developing preventive and treatment strategies for dealing with this too common health problem.